Move device ports to device/testing/*

This is a first step to implement the proposal in https://gitlab.com/postmarketOS/postmarketos/issues/16 for https://gitlab.com/postmarketOS/postmarketos/issues/11.

All device ports must now be under a subdirectory of device, e.g. device/testing. At the moment none of these subdirectories is handled in a special way. I would suggest that we keep all devices in device/testing/* for now and merge this early, so it becomes more easy to work on the upcoming changes (i.e. allowing to move devices to main or community).

(Otherwise I always have to move all device ports in my local pmaports clone only to test my changes...)

The first commit should not be merged (a HACK to let CI pass by moving all devices to device/testing after cloning pmaports...)